1. Field of the Invention
Quaternary ammonium salts or "compounds" are tetrasubstituted ammonium salts. They have a large number of commercial applications, including uses as ingredients for fabric softeners, as reaction materials in the manufacture of organophilic clays, as cosmetic ingredients, and as bactericidal agents. The chemical reaction processes used to synthesize quaternary ammonium compounds normally require the use of a non-reactive solvent to reduce the viscosity of the amines, particularly tertiary amines, prior to and during quaternization. The solvent most often employed commercially is isopropyl alcohol ("IPA"). Upon completion of the quaternization reaction process, the resulting quaternary ammonium compounds remain in solution, and are commonly sold as quaternary ammonium compositions in such a solvent mixture, or are dried, ground and then sold as relatively solvent-free powders.
In many applications using quaternary ammonium compounds the presence of solvents such as isopropyl alcohol diminishes the desired performance of the quaternary compound and adds environmental and manufacturing hazards due to the isopropyl alcohol's flammability, volatility and toxicity. Drying techniques have been developed which are capable of removing isopropyl alcohol from certain quaternary--solvent mixtures, but are not generally employed, because they add significant manufacturing costs, while failing to remove all of the isopropyl alcohol.
2. Summary of the Invention
The present invention involves the discovery that quaternary ammonium compounds, synthesized using specified diluents, provide improved properties and possess numerous advantages over essentially identical quaternary ammonium compounds quaternized using isopropyl alcohol or other prior art solvents. Quaternary manufacturers employing the new invention, in addition to obtaining superior products, will also obtain the flexibility to utilize specific diluents selected either to promote beneficial effects in the ultimate product from the presence of the novel diluent, or at a minimum, to avoid existing deleterious effects on the systems of quaternary ammonium compound applications caused by IPA contamination. Such use will also lead to improved product handling properties by significantly reducing the flammability, toxicity and environmental hazards associated with quaternary ammonium compounds made and sold with traditional volatile vehicles, and will open new markets to such products. Particularly beneficial uses are in providing ways of making improved organoclays, cosmetic products including shampoos, and fabric softeners, as well as new uses of quaternary ammonium compounds as additives for the deinking of wastepaper pulp and as surfactants for laundry products.
3. Description of the Prior Art
Quaternary Ammonium Compounds
Quaternary ammonium compounds (sometimes abbreviated as "quats") of the type useful in this invention typically are salts of organic cations which have a positive charge localized on a single nitrogen atom and a charge neutralizing anion designated M.sup.-.
Quaternary ammonium compounds have the following formula: ##STR1## These quaternary ammonium compounds may be described as having four moieties where R is an organic radical and R.sup.I, R.sup.II and R.sup.III, the remaining groups attached to the central nitrogen atom, are typically selected from the group consisting of (a) alkyl groups; (b) aralkyl groups which are benzyl and substituted benzyl moieties; (c) aryl groups such as phenyl; (d) beta, gamma-unsaturated groups having six or fewer carbon atoms, (e) hydroxyalkyl groups having 2 to 6 carbon atoms; and (f) hydrogen. The principal groups above are most often derived from naturally occurring fats or oils such as tallow, corn oil, soybean oil, cottonseed oil, castor oil, linseed oil, safflower oil, palm oil, peanut oil and the like. Mixtures of oils are commonly employed. The oil may be of natural sources, or a synthetic version of same, or modifications of a naturally occurring oil using known techniques. A broad listing of the useful components used to make quaternary ammonium compounds ("quats") is described in U.S. Pat. No. 5,336,647.
M.sup.- is an anion which usually is chloride, methyl sulfate, bromide, iodide, hydroxyl, nitrite or acetate. The anion accompanying the organic cation is selected so as not to affect adversely the intended use of the quaternary ammonium compound, and may optionally be selected to impart unique characteristics to the quaternary compound.
Commercially significant quats usually contain at least one residue of a naturally occurring oil, most often derived from beef tallow. In addition to the uses previously mentioned, these quaternary ammonium compounds also find utility as surfactants, anti-static agents, flotation agents, biocides, and, as stated, as reactants in the formation of organically-modified clay rheological control additives for paints, coatings, drilling muds and the like. In addition, poly-quaternary compounds with more than one nitrogen atom have been utilized and are included in the definition of quaternary ammonium compounds.
Processes of Making Quaternary Ammonium Compounds
The manufacture and preparation of quaternary ammonium compounds is achieved by techniques well-known in the art. When preparing a quaternary ammonium salt, one skilled in the art can prepare a dialkyl secondary amine, for example, by the hydrogenation of nitriles, and then form the methyl dialkyl tertiary amine by reductive alkylations using formaldehyde or dimethoxymethane as a source of the methyl radical. A commercial manufacturing process typically involves various stages, including those resulting in the creation of nitriles, primary amines, secondary and tertiary amines, and finally the quaternary compound itself.
The manufacturing process generally involves saturation of fatty acids derived from tallow, or of a commercial natural oil, by hydrogenation as an early step. This has led manufacturers to use the term, "hydrogenated tallow", or "HT", when describing common quaternary ammonium compounds, even those not exclusively derived from tallow fatty acids. Saturated, relatively long-chain hydrocarbon molecules are typically solids or very highly viscous liquids at room temperatures. They may be liquified by heating, but, particularly as the molecular weight of the intermediate products is increased in the course of the manufacturing process, the heat-induced liquification will not compensate for increasing viscosity, which will inhibit subsequent manufacturing steps. Accordingly, the quaternization step typically has been done in a liquid medium in order to solvate and reduce the viscosity of the both the starting material and the reaction products, and to reduce foaming. The medium used for commercial processing has almost universally been isopropyl alcohol (IPA).
Quaternization reactions are typically carried out in the presence of an inorganic alkali--such as sodium bicarbonate, sodium hydroxide, sodium or calcium carbonate--to react with any acid that may be formed as a by-product from the reaction of the alkylating agent (typically an alkyl or aralkyl halide) with labile hydrogen compounds contained within the reaction mixture. Such acidic materials form salts with the amine reactant, deactivating it toward quaternization. Such labile hydrogen compounds include, but are not limited to, primary and secondary amines--typically from incomplete reductive alkylation of the amine in the preceding step--water, and, when an alcoholic diluent is used as the reaction medium, the reaction solvent itself. Thus, while a chemical such as isopropanol will generally serve to accelerate the reaction of the alkylating agent with the amine and the reaction of any acidic by-products with the inorganic alkali, it will also reacts with the alkylating agent to generate unwanted acidic compounds and consumes the alkylating agent.
After manufacture, unless expensive vacuum distillation or freeze drying and grinding processes are later performed to produce a powdered product, the commercial quaternary ammonium compound is then generally sold in IPA solution, with typical activities ranging from 25 to 85 percent quaternary ammonium compound. Customers typically have no commercial use for the IPA either when blending the quat (or similar product) in the customer's process or product, such as fabric softener manufacture, or when using it as a reactant, for example in the manufacture of organoclays. Organoclays are the reaction product of smectite-type clay and quaternary compounds. See for example U.S. Pat. No. 4,105,578. The IPA often is discharged into a sewer leading either to a publicly owned water treatment facility or to a permitted direct discharge, or is volatilized and exhausted to the atmosphere when the organoclay is dried. As an alternative, significant expenses may be incurred for capture and reuse of the IPA from the effluent or pre-atmospheric emissions. As environmental controls on indirect dischargers, direct permitted dischargers, and emitters of volatile organic contaminants ("VOC's") are tightened, the cost of IPA disposal has been increasing at a rate several times that of inflation.
Several prior art references describe the various media, including IPA, which have been used to provide the volatile liquid solvent vehicle for quaternary ammonium compound manufacture. U.S. Pat. No. 2,775,617 describes a process for the preparation of defined quaternary ammonium compounds using animal fat tallow oils as starting ingredients. The patent describes the preparation of quaternary ammonium compounds and more particularly the preparation of tetra-alkylammonium compounds by the alkylation of alkyl secondary amines with alkyl halides. The patent teaches the use of the lower alcohols, particularly n-butanol, as solvent media for the reaction. U.S. Pat. No. 2,644,003 describes the making of quaternary ammonium compounds having very strong bactericidal activity using, as the reaction solvents, benzene, toluene, xylene, acetone, ethyl and butyl acetate. The compounds are useful for the disinfection of human skin, as well as the disinfection of utensils including medical instruments. U.S. Pat. Nos. 2,950,318 and 3,175,008 relate to improved processes for the production of quaternary ammonium compounds employing, as the solvent vehicle, one of the low-boiling alcohols including methanol, ethanol, propanol, isopropanol, butanol, isobutanol, and the like, with the preferred solvent being isopropyl alcohol, together with a minimum amount of water. Upon completion of the reaction, the mixture produced contains the quaternary compound in an aqueous alcoholic solution. While not commercially significant certain quaternary manufacturers have made their products in glycols as the solvent including propylene glycol, hexylene glycol and diethylene glycol.
Relatively recent U.S. Pat. No. 4,857,310 shows the preparation of quaternary ammonium compounds from cosmetic and toiletry compositions from castor oil triglycerides carried out using, in one stage, solvents such as toluene, chloroform and dichloromethane, and in a second stage, the organic vehicle ethanol introduced at an elevated temperature. The resulting product is then dried under vacuum at 80.degree. C. to remove the ethanol.
The media described in the prior art, in the main, involve mostly volatile organic compositions which share a number of properties, the most important of which is the low temperature at which they exhibit a vapor pressure of approximately 1 mm. For example ethanol exhibits a vapor pressure of 1 mm, at a temperature of -31.degree. C. while toluene's temperature is -26.7.degree. C. and methanol's is -44.degree. C. While glycols have vapor pressure-higher temperatures, they present problems of toxicity, odor, flammability and solubility in water systems where the quaternary may be used, that they have not been widely used. Most of the solvents employed in the conventional manufacture of quaternary ammonium compounds can be further characterized as having toxicity, low viscosity, low flash and freezing points. In particular, the vapor pressure of almost all the prior art vehicles substantially exceeds 1 mm of Hg at 25.degree. C.
Quaternary ammonium compounds are usually prepared in complex and expensive stainless-steel or glass-lined equipment. The amine, with or without water, is loaded into the reactor and heated to the proper temperature (usually 80.degree.-100.degree. C.), and an alkylating reagent is added. Quaternization of tertiary amines with alkyl halides is bimolecular. The rate of reaction is influenced by a number of factors, including the nature and quality of the starting materials, the basicity and nucleophilicity of the amine, stearic effects, temperature, reactivity of the halide, and the polarity and other characteristics of the solvent used. Such solvents, in addition to providing liquidity, also assist the reaction by stabilizing the ionic nature of the transition stage of the quaternization reaction.
Uses of Quaternary Ammonium Compounds
The use of quaternary ammonium compounds to make organophilic clays is described in a large number of patents. Illustrative patents which describe such organophilic clays and their use as thickeners and rheological additives include U.S. Pat. Nos. 4,894,182, 4,450,095 and 4,434,075. Organoclays are the reaction products of smectite clays, including hectorite and bentonite, with one or more quaternary ammonium compounds.
Volume 19 of the Encyclopedia of Chemical Technology at pages 529 to 530 describes the various uses of quaternary ammonium compounds as fabric softeners. There are three types of commercial products disclosed: the first is a 4-8 wt % dispersion of quaternary ammonium compound, which is added to the rinse cycle of the washing process by the washing machine user. The second commercial product is a quaternary ammonium compound formulation applied to a nonwoven sheet or a polyurethane foam, which is added with the wet clothes into the dryer by the homemaker. This product formulation contains a transfer agent, usually a fatty-acid ester, which allows the quaternary ammonium compound to transfer from the substrate to the wet clothes. The third type of product is a combined detergent, softener and antistatic formulation containing quaternary ammonium compounds, which allows the introduction of all necessary ingredients into the wash cycle of the washing process. In all cases, the benefits to the user are fabric softening, antistatic properties, ease of ironing, and odor improvement, the latter because of the common addition of perfumes to the formulation. The most widely used, and most effective, quaternary ammonium compounds used for fabric softening purposes are the dimethyl bis[hydrogenated tallow] ammonium chlorides and methyl sulfates ("2M2HT").
Another significant use for quaternary ammonium compounds is in certain cosmetics, particularly for hair treatment. Quaternaries have a high affinity for proteinaceous substrates, and this property makes them useful for hair treatment. They impart antistatic effects, increase hair wetting, improve wet and dry combing, and improve feel and luster. Other cosmetic uses are widely diversified, and the quaternary ammonium compound formulations vary from one cosmetic manufacturer to another, depending on the qualities to be emphasized. In some cases, the solvent with the quaternary ammonium compound is acceptable, while in others it must be removed, for example, by spray drying.
Another important use of quaternary ammonium compounds is in compositions for deinking wastepaper, which is a growing industry both in the United States and throughout Europe. Applicant's assignee in pending U.S. Pat. No. 5,336,372 describes a process for deinking wastepaper in an aqueous flotation process utilizing organoclays formed in situ in the deinking apparatus by the use of quaternary ammonium compounds as deinking chemicals, particularly 2M2HT. U.S. Pat. No. 4,935,096 discloses a method for deinking waste printed paper by using quaternized alkyl tallow compounds as deinking surfactants in a washing process. Since quaternary compounds in commercial use contain IPA, or other similar soluble solvents such as hexylene glycol, the constantly recycled water used in commercial deinking can be adversely impacted by present-day compositions, since the increasing concentrations of such solvents result in process difficulties, solvent build-up and disposal problems, and eventually lead to discharge into the environment.